<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>深度监视</title>
    <script src="../js/vue.js"></script>
  </head>
  <body>
    <div id="root">
      <h2>今天天气很{{info}}</h2>
      <button @click="changeWeather">切换天气</button>
      <hr />
    </div>

    <script>
      Vue.config.productionTip = false;

      const vm = new Vue({
        el: "#root",
        data: {
          isHot: true,
        },
        computed: {
          info() {
            return this.isHot ? "炎热" : "凉爽";
          },
        },
        methods: {
          changeWeather() {
            this.isHot = !this.isHot;
          },
        },

        watch: {
          //正常写法
          /*
          isHot: {
           //immediate:true,//初始化时让handler调用一下
           //deep:true,//深度监视
           handler(newValue,oldValue){
            console.log('isHot被修改了',newValue,oldValue);
           }
          },
          */
          //简写
          isHot(newValue, oldValue) {
            console.log("isHot被修改了", newValue, oldValue);
          },
        },
      });
      //正常写法2
      /*
      vm.$watch("isHot", {
        //immediate:true,//初始化时让handler调用一下
        //deep:true,//深度监视
        handler(newValue, oldValue) {
          console.log("isHot被修改了", newValue, oldValue);
        },
      });
      */

      //简写2
      /*
      vm.$watch('isHot',fuction(newValue,oldValue){
        console.log("isHot被修改了", newValue, oldValue);
      })
      */
    </script>
  </body>
</html>
